Edge-lit signs of the type referred to will be familiar to many, at least in England, from their use in cinemas and theatres to indicate exits or emergency exits. Such signs typically have a sign board of glass or transparent plastics material which is etched or otherwise marked with, for example, the word "EXIT". The sign is often suspended from a light box which contains a fluorescent tube or other light source, and light from that source enters the edge of the sign board and is refracted at the etched wording to render it visible in the darkened auditorium.
The light box required for illuminating such a sign is rather bulky and the necessity for its employment inhibits the use of edge-lit signs in many environments where they may be useful.
It is an object of this invention to remedy this disadvantage, and accordingly the present invention provides an edge-lit sign comprising a light-transmitting sign board bearing sign information adapted to be illuminated by light entering the board through an edge, characterised in that there is provided at least one strip of electro-luminescent sandwich material which extends along at least a part of the length of said edge of the sign board and which is arranged and energisable to illuminate the sign.
Electro-luminescent sandwich material can be made in thin strip form, for example about 0.5 mm thick, and 10 mm or less in width. It will be appreciated therefore that such a strip can be used for edge-lighting a sign without the need for a light box or indeed any frame which has significantly greater width than the thickness of the sign board plus any frame lips, and there is no reason why such frame lips should be any thicker than 0.5 mm or so.
In fact, electro-luminescent sandwich material has been available for many years, but its uses to date have been surprisingly limited having regard to its potential advantages in many fields of use.
The present invention is based on an appreciation of these advantages and an insight into ways in which these advantages may be exploited.
Electro-luminescent material with which the present invention is concerned has essentially a layer of a phosphor which is sandwiched between a pair of electrodes of which at least one is translucent. When an electrical potential is applied between the electrodes, the phosphor layer becomes excited and light is emitted. Given a uniform layer, the flux density of the emitted light is uniform over the full extent of the layer. The electrodes and phosphor layer (the "working layers") are sandwiched between outer layers which serve to support and protect the working layers and any other layers which may be present.
The light output can be uniform over a strip length which can be as large or as small as required, and it is economical. A single strip may be used along just one edge of a sign board, or it may surround substantially the whole periphery of the board. Alternatively, a plurality of strips may be laid up against different sections of the periphery of the board. It will be appreciated that if an electro-luminescent strip is to be bent at a corner of the board, the radius of curvature of the strip at that corner should not be so small as to give significant risk of breakage to damage to the strip such as would render it inoperable. It is presently believed that any radius of curvature above 1 cm could be acceptable given suitable choice of the supporting plies of the electro-luminescent sandwich.
The sign board may be formed of glass or plastics material. If the board is intended for viewing from both faces, it is suitable to form the board as a laminate which has a central opaque ply. This allows such asymmetrical signs as EXIT signs to be read from both signs without the display becoming garbled.
Of course the sign could be some form of symbolic direction indicating sign or other sign intended for reading from both sides, or it could be intended for positioning so that it could be read from one side only, in which cases the board could be constituted by a simple sheet.
In some particularly preferred embodiments of the invention, the sign board is formed as a shelf. In such embodiments, the display material might for example be constituted by the brand name of goods displayed on the shelf.
In such embodiments it may be convenient to mount the electro-luminescent material so that it is carried by a support for the shelf rather than by the shelf itself. In this way, the lighting apparatus may be set up permanently, and shelves substituted as desired without the inconvenience of having to dis-connect and re-connect the lighting strip to a source of current.
The required display material is suitably mechanically etched or moulded into the sign board. The advantages of this can be great, since in particular, the etching or moulding can be such as to cause the etched or moulded design to refract light emitted by the electro-luminescent strip and thus the actual display material itself may be caused to emit light, rather than being merely back-lit. This affords the designer of the display material a much greater freedom to exercise his or her talents in order to attract attention to the signed message or thing, and this is particularly important and advantageous in the field of advertising.
The electro-luminescent sandwich itself may be directly applied to the sign board for forming the display, and the electro-luminescent strip material may thus be in the form of a sandwich having a ply which is coated with an adhesive and which is covered with a peelable protective covering prior to use.
The phosphor layer of electro-luminescent material for use in the invention may be excited by an applied potential of less than 150 v, and such potential may be as low as for example 5 v which is advantageous from the point of view of safety and convenience if it is desired to power the display using batteries. The power may be AC or DC, and it may be supplied from the mains (for example via a transformer) or from batteries. The use of a pulsed supply to cause flashing of the phosphor will have particularly advantageous attention-seeking properties.